Macerated Monozygotic Twins in Quadruplet Pregnancy of the Cape hyrax (Procavia capensis)

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Two macerated monozygotic twins associated with two live fraternal twins in a pregnant hyrax are reported. The identical twins had a single, monozonary, infarcted placenta and corresponded to one corpus luteum in the homolateral ovary, whereas the fraternal twins with two placentas had two corpora lutea in the opposite ovary. The Cape hyrax (Procavia capensis) has been recommended as an animal of potential value for medical research in the study of gastric ulcer (Griner, 1968) . They resemble rodents only superficially but are placed more closely to the Proboscidea in taxonomic position, in a separate Order, the Hyracoidea, because of characteristics of their feet and the large bulge of the anterior maxillary skull, placentation, etc. Most litters of the hyrax at the San Diego Zoo have been born during May and June and the gestational period of the hyrax is estimated to be 7 1/2 months (Griner, 1968) . THURSBY-PELHAM (1924) pointed out that the hyrax placenta has a zonary form and a certain resemblance to that of the elephant. WISLOCKI and WESTHUYSEN (1940) described the placenta and fetal membranes of Procavia in greater detail and also suggest that the elephant and the manatee exhibit very close structural placental affinities. Placentation is characterized as chorioallantoic, labyrinthine and of the hemochorial type (WISLOCKI and WESTHUYSEN, 1940) . The usual litter size of hyrax varies from one to six, the average being three (GRINER, 1968) . The distribution of the embryos in the uterus and their relationship to the corpora lutea in the ovaries of pregnant Procavia has been described as usually homolateral (WISLOCKI and WESTHUYSEN, 1940), that is to say, the number of corpora lutea in one ovary usually corresponds to the number of embryos of the uterine horn on the same side. Exceptions, however, were recorded and“internal migration”is a suggested explanation. No information concerning the occurrence of identical twins in the hyrax has been recorded. This report describes the uterus of a pregnant hyrax in which one horn contained fraternal twins with two independent placentas, whereas the opposite horn held presumably monozygotic twin fetus papyracei with a single placenta. There were two corpore lutea in the first ovary and only one in the second.
日本哺乳類学会の論文

Macerated Monozygotic Twins in Quadruplet Pregnancy of the Cape hyrax (<I>Procavia capensis</I>)

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